1. Field of the Invention
The present invention relates to a method for recovering liquid chlorine derivatives of hydrocarbons, and namely to a method for recovering chlorine derivatives of hydrocarbons from difficultly volatile impurities such as residues of a Friedel-Crafts catalyst, and resinous substances.
Chlorine derivatives of hydrocarbons are widely used as both solvents and intermediates in organic synthesis. Heavy demands are placed upon chlorine derivatives of hydrocarbons with respect to the content of catalytically active impurities and resinous substances. Therefore providing methods for recovering chlorine derivatives of hydrocarbons, ensuring a high quality of the end product is an important problem.
2. Description of the Prior Art
Known in the art is a method for recovering methyl chloroform (see British Pat. No. 930,172) comprising a Friedel-Crafts catalyst. This method for recovering methyl chloroform is carried out in a reactor wherein water is fed which is then heated to a temperature of 85.degree. C. Thereafter methyl chloroform and ammonia are fed into the reactor, the ammonia being in an amount of 0.004 to 0.006 parts by weight per 1 part by weight of methyl chloroform. Shortly after being introduced into the 85.degree. C. water, the methyl chloroform, having a boiling temperature of 74.1.degree. C., soon boils. In the course of the recovery process, ferric chloride and hydrogen chloride contained in the methyl chloroform react with ammonia, and the vapors of methyl chloroform are condensed at a pH being within the range of 6 to 12. The condensate is then dried and rectified.
However, the use of the above method causes the wetting of the recovered methyl chloroform and its contamination with ammonia, which makes it necessary to later purify the methyl chloroform of ammonia.
In another method described in F.R.G Patent No. 1,235,878 ammonia is again used to purify methyl chloroform of catalysts. Known in the art is a method of purifying liquids of difficultly volatile impurities by distillation (A. G. Kasatkin, Osnovnye protsessy i apparaty khimicheskoi tekhnologii, Moskva, Khimia Publishers, 1971, pp. 393-397, 496-546). The recovery process resides in that the liquid containing difficultly volatile impurities is heated in a reaction vessel up to the boiling temperature of the end product. In so doing the liquid being recovered evaporates, the vapors pass through a condenser and condense therein, and the condensate is collected in a receptacle. The difficultly volatile impurities remain in the reaction vessel.
However, the above-described method involves prolonged heating of the liquid being recovered, which leads to decomposition of the end product. In addition, heating the liquids in the presence of catalyst residues leads to an increase in the amount of resinous substances. In view of the fact that the boiling temperature of the resinous substances is appreciably higher than that of the product being recovered, and both the liquid being recovered and the resinous substances are mutually soluble, the increase in the degree of evaporation requires that the temperature within the reactor be considerably higher than the boiling temperature of the end product. This will lead to a higher extent of decomposition of the substance being recovered and to an increase in the amount of resinous substances. The term "degree of evaporation" is used herein to denote the amount of the evaporated product and the initial amount of the product.
The method can also be carried out by evaporating a liquid from a film of an inert liquid. When using rotary film-type evaporators, the degree of evaporation increases. However, in this case the residue left after the distillation process comprising bottoms of a catalyst and resinous substances is a viscous resin which adheres to the evaporator surface on which evaporation of the liquid being recovered occurs. This leads to an uncontrollable increase in the thermal resistance of the heat exchange surface. In addition, the procedure of cleaning the heating surface from residues of a catalyst and resin is complicated and labor-consuming.
The principal object of the present invention is to provide a method of recovery of liquid chlorine derivatives of hydrocarbons which makes it possible to reduce the degree of decomposition of a product being recovered and at the same time to reduce the residues of catalyst and resinous substances.